Characterization of spoilage bacteria in pork sausage by PCR-DGGE analysis

Microbial community structure and biogenic amines content variations in chilled chicken during storage

The aim of this study was to investigate the sensory indicators, biogenic amine contents, and bacterial community structure and diversity of chilled chicken stored at 4°C under aerobic conditions. Bacterial diversity and dominant bacteria were analyzed using high-throughput sequencing technique (HTS). The relationship between biogenic amine contents and microbial community structure was studied. The results showed that contents of putrescine and cadaverine increased significantly with storage time. Proteobacteria was absolutely dominant flora at the phylum level. The predominant spoilage bacteria found in chicken thighs were Pseudomonas, Acinetobacter, Aeromonas, Shewanella, and Yersinia, and the difference with chicken breasts was related to the presence of Myroides and absence of Yersinia. Myroides, Yersinia, and Shewanella were reported for the first time as an important contributor to the spoilage-related microflora. Bacterial diversity and richness indices showed fluctuating and decreasing trend with storage time. The redundancy analysis showed that the relative abundance of Pseudomonas, Yersinia, and Janthinobacterium was positively related to the contents of putrescine, cadaverine, and tyramine, while Shewanella and Aeromonas showed positive relationship with putrescine content. Furthermore, positive relationship of Myroides and Desulfovibrio with the contents of cadaverine and tyramine was proposed for the first time. The key findings of this study can provide experimental data for food safety monitoring during refrigerated storage and preservation for poultry meat products.

Active edible films based on green tea extract and gelatin for coating of fresh sausage

The objective of this work was to develop, characterize and evaluate the application of active edible films based on gelatin and green tea extract in coating of fresh sausages. The green tea extract showed IC50 of 0.088 mg/mL and minimum inhibitory concentrations of 0.05 mg/mL for Listeria monocytogenes, 0.025 mg/mL for Staphylococcus aureus, 0.04 mg/mL for Escherichia coli, and >1.0 mg/mL for Salmonella enterica serovar Choleraesuis. The formulation with 15% (w/v) of gelatin and 30% (w/w) of glycerol showed better adhesion and appearance in the coating of the product. When using 1.0% of green tea extract, the lowest IC50, was obtained and the antioxidant activity was maintained for 35 days. There was a more accentuated decrease in pH and an increase in acidity and peroxide index in fresh sausages without film compared to those coated with the active film (1.0% of green tea extract) during storage. In addition, it was found that the use of active gelatin film (1.0% of green tea extract) kept the TBARS indexes of fresh sausage samples lower than the standard (without coating) and of films containing only gelatin, after 48 days of storage.

Microbial Growth and Biogenic Amine Production in a Balkan-Style Fresh Sausage during Refrigerated Storage under a CO2-Containing Anaerobic Atmosphere: Effect of the Addition of Zataria multiflora Essential Oil and Hops Extract

Fresh sausages are highly perishable, and the preservatives allowed in these types of meat preparations are limited. Balkan-style fresh sausages were prepared in triplicate without antimicrobials (Control), with an aqueous hops extract (30 mL/kg), with Zataria multiflora Boiss essential oil (1 mL/kg), or a combination of both (15 and 0.5 mL/kg, respectively), and refrigerator-stored under a 20% CO₂ and 80% N₂ atmosphere. The spoilage microbial growth, i.e., lactic acid bacteria (LAB), Brochothrix thermosphacta, Enterobacteriaceae, Micrococcaceae, molds and yeasts, the pH value, and the production of biogenic amines in the sausages were monitored weekly and compared with a control sausage during a 35-day storage period. Furthermore, 349 colonies of presumptive LAB (isolated from the De Mann, Rogose-Sharpe agar plates) were identified using a MALDI-TOF-based method. Growth levels to ≈ 9 Log colony forming units (CFU) per g were reached by LAB, with a predominance of Lactobacillus sakei. Enterobacteriaceae and B. thermosphacta also showed significant growth (up to 6 Log CFU/g). Biogenic amine levels increased, and tyramine values overcame 250 mg/kg. The study could not demonstrate a significant effect of antimicrobial source treatments in any of the characteristics studied, and thus, the shelf-life of sausages.

Application of nisin as biopreservative of pork meat by dipping and spraying methods

Comparison between dipping and spraying methods to inhibit bacterial growth on artificially contaminated pork meat showed greater effectiveness of the latter method during the whole low-temperature one-week storage of product. These results suggest that the spraying method could be successful in directly applying antimicrobials to food products.

Developing novel species-specific DNA markers for PCR-based species identification of the Lactobacillus sakei group

Identification of members of the Lactobacillus sakei group (LSG) by common phenotypic and genotypic methods is generally inadequate and time-consuming. The objective of this study was to develop novel species-specific primers based on sequence-characterized amplified region (SCAR) markers using random amplified polymorphic DNA polymerase chain reaction (RAPD-PCR) analysis. Three species-specific fragments were gel-purified, cloned and sequenced after preliminary screening of 80 random primers. Accordingly, three pairs of primers Lcur-F/R, Lgram-F/R and Lsakei-F/R were designed based on single species-specific bands (281, 278 and 472 bp) that were obtained from Lactobacillus curvatus, Lactobacillus graminis and L. sakei, respectively. The specificities of these primer pairs were confirmed in 21 LSG strains and 31 nontarget Lactobacillus strains. In addition, the detection limits for each primer pair were approx. 10⁵ , 10⁴ and 10⁶ cells per gram of meat samples spiked with L. curvatus, L. graminis and L. sakei, respectively. In conclusion, we have successfully developed a rapid, accurate and effective PCR-based method for identification of species in the LSG.

SIGNIFICANCE AND IMPACT OF THE STUDY

Neither phenotypic nor the most commonly used genotypic method (16S rRNA gene sequencing) provides sufficient resolution for accurate identification of the Lactobacillus sakei group. A sequence-characterized amplified region method developed in this study provides a rapid, cost-effective way to detect the member of the L. sakei group in meat sample.

The sensory quality of allergen-controlled, fat-reduced, salt-reduced pork-ostrich sausages during storage

BACKGROUND

New meat products tailored to consumer health should be characterised by reduced sodium, fat and cholesterol contents and other health-promoting benefits. However, the food sector's greatest challenge is allergen-free production. Consumers are not willing to compromise the sensory quality of meat products for health. The aim of the present study was to analyse the influence of the storage time on the physical properties and consumer acceptance of allergen-controlled, fat-reduced, salt-reduced pork-ostrich sausages. The study focused on pork-ostrich sausages produced in accordance with a new patented technology, which focused on eliminating cross-contamination on-line in the plant, eliminating cross-contamination after preparation, and eliminating spices with high allergy potential. The production was focused on reducing fat (by approximately 50%) and salt (by approximately 30%) levels.

RESULTS

No changes in the texture parameters of the sausage were observed during storage time; however, some changes in colour were observed. There were no significant differences in sensory consumer acceptability of pork-ostrich sausage after 14 days of storage; thus, it may be stated that the instrumentally assessed differences in colour did not influence consumer acceptance.

CONCLUSION

The applied fat and NaCl reduction in the pork-ostrich sausages contributed to high consumer ratings and was not correlated with saltiness acceptability. © 2017 Society of Chemical Industry.

Active starch biopolymeric packaging film for sausages embedded with essential oil of Syzygium aromaticum

Starch polymer matrices were developed with the incorporation of 1% clove essential oil (EO) (Syzygium aromaticum) aiming for use as active packaging for sausages. At the concentration of 1% EO in the polymer matrix, it showed exponential behavior with respect to oil release over 30 days, with faster release in the beginning and a tendency towards a reduction in release velocity over time. The presence of OE in the biofilm led to significant differences versus the control in terms of aroma and flavor parameters. It was found that EO had an antioxidant effect in sausages with a significant difference between treatments with respect to TBA (thiobarbituric acid) values at the end of a 15 day period of refrigerated storage. There were no significant variations in pH and Aw among treatments during the evaluated period. A significant negative correlation (-0.78) between brightness (L*) and the lipid oxidation of the products was observed.

Agricultural by-products with bioactive effects: A multivariate approach to evaluate microbial and physicochemical changes in a fresh pork sausage enriched with phenolic compounds from olive vegetation water

The use of phenolic compounds derived from agricultural by-products could be considered as an eco-friendly strategy for food preservation. In this study a purified phenol extract from olive vegetation water (PEOVW) was explored as a potential bioactive ingredient for meat products using Italian fresh sausage as food model. The research was developed in two steps: first, an in vitro delineation of the extract antimicrobial activities was performed, then, the PEOVW was tested in the food model to investigate the possible application in food manufacturing. The in vitro tests showed that PEOVW clearly inhibits the growth of food-borne pathogens such as Listeria monocytogenes and Staphylococcus aureus. The major part of Gram-positive strains was inhibited at the low concentrations (0.375-3mg/mL). In the production of raw sausages, two concentrates of PEOVW (L1: 0.075% and L2: 0.15%) were used taking into account both organoleptic traits and the bactericidal effects. A multivariate statistical approach allowed the definition of the microbial and physicochemical changes of sausages during the shelf life (14days). In general, the inclusion of the L2 concentration reduced the growth of several microbial targets, especially Staphylococcus spp. and LABs (2log10CFU/g reduction), while the increasing the growth of yeasts was observed. The reduction of microbial growth could be involved in the reduced lipolysis of raw sausages supplemented with PEOVW as highlighted by the lower amount of diacylglycerols. Moisture and aw had a significant effect on the variability of microbiological features, while food matrix (the sausages' environment) can mask the effects of PEOVW on other targets (e.g. Pseudomonas). Moreover, the molecular identification of the main representative taxa collected during the experimentation allowed the evaluation of the effects of phenols on the selection of bacteria. Genetic data suggested a possible strain selection based on storage time and the addition of phenol compounds especially on LABs and Staphylococcus spp. The modulation effects on lipolysis and the reduction of several microbial targets in a naturally contaminated product indicates that PEOVW may be useful as an ingredient in fresh sausages for improving food safety and quality.

Spoilage potential of Vagococcus salmoninarum in preservative-free, MAP-stored brown shrimp and differentiation from Brochothrix thermosphacta on streptomycin thallous acetate actidione agar

AIMS

During a previous study concerning brown shrimp (Crangon crangon), selective streptomycin thallous acetate actidione (STAA) agar was used to determine the growth of Brochothrix thermosphacta. However, the growth of Vagococcus salmoninarum on this medium was also noticed. This study explores the spoilage potential of this organism when inoculated on sterile shrimp.

METHODS AND RESULTS

Isolates growing on STAA were identified using (GTG)5 clustering followed by partial 16S rRNA gene sequence analysis. Their biochemical spoilage potential was analysed for H2 S production and enzymatic activities were tested using an APIZYM test. Headspace solid phase micro-extraction (SPME) and gas chromatography-mass spectrometry (GC-MS) were used to analyse the volatile organic compounds (VOCs) produced during storage of inoculated shrimp.

CONCLUSION

Fifty-five per cent of isolates taken from STAA could be identified as V. salmoninarum, while no apparent morphological difference with B. thermosphacta isolates was identified upon the prescribed incubation conditions. For isolates identified as V. salmoninarum, production of 2-heptanone, 2-nonanone, 2-undecanone was found, as was the possibility to form H2 S.

SIGNIFICANCE AND IMPACT OF THE STUDY

When using the STAA medium for detecting B. thermosphacta, one should consider the possible abundant presence of V. salmoninarum as well. Based on this study, V. salmoninarum does not exhibit great spoilage potential, although it can produce H2 S and formed VOCs which are also found in other spoiled seafood products.